The present invention relates to the field of short circuit protection circuitry, and in particular, to a discharge interrupt circuit capable of operating at a low supply voltage.
An integrated circuit is often constructed from a small chip of semiconductor material upon which an array of active/passive components have been constructed and connected together to form a functioning circuit. The integrated circuit is generally encapsulated in a plastic housing (chip) with signal, power supply, and control pins accessible for connection to external electronic circuitry. Input signals transmitted to the integrated circuit via selected input pins are processed by active and passive components that are designed with a limited range of supply voltages available for optimal performance.
Battery-powered devices often employ integrated circuitry to regulate the power provided by a battery cell. Linear voltage regulators are often used where the input power source is unregulated or clean power is required in a noisy environment. A linear voltage regulator may use an amplifier to attenuate the supply voltage.
Non-ideal properties may have little or no impact when a circuit is operating at the rated supply voltage. However, when the supply voltage sags to a level far below the rated supply voltage, these non-ideal properties may have a larger impact. An example of a non-ideal property is the associated impedances of transistors, and a battery cell in a circuit. The negative impact of the voltage divider created by these impedances on the operation of the circuit can increase when the supply voltage sags.
For example, when the battery is shorted to ground, an undesirable, large discharge of current can occur. A short circuit event can occur faster than a regulatory circuit can react to the event. The performance of the regulator circuit can be affected and the discharge of current may itself cause a sag in the supply voltage. In addition, the discharge of current may itself cause a sag in the supply voltage. Also, a shorted battery cell may be inadequate to supply power to operate the circuit.
The invention is directed to a discharge interrupt circuit that provides short circuit protection for a regulator circuit that includes a load regulation device. The discharge interrupt circuit detects a high output current or short circuit condition in the device and diverts the output current from the load by deactivating the device. Logic included in the discharge interrupt circuit is arranged to return the device to normal operation once the short circuit condition is removed. The discharge interrupt circuit provides short circuit protection that can operate at low power supply voltages.
Briefly stated, a discharge interrupt circuit and method is directed to short circuit protection for an electronic circuit that includes a load regulation device that is arranged to normally provide an output current. The discharge interrupt circuit detects a short circuit condition by monitoring the drain-source voltage across the load regulation device. When a short circuit is detected, a logic circuit within the discharge interrupt circuit latches the short circuit condition in a memory circuit and disables the load regulation device such that the output current is interrupted from flowing. The logic circuit re-enables the load regulation device when the logic circuit has determined that the device has been deactivated. A time-out circuit can also be used add an additional delay between the load regulation device being disabled and re-enabled. The discharge interrupt circuit provides short circuit protection with power supply voltages less than 1V.
In an embodiment of the invention, an apparatus provides over-current protection to a regulator circuit that includes a load regulation device. The load regulation device is arranged to regulate a current flow through the load regulation device from a power source in response to a control signal that is produced by a control circuit. A sensor circuit is configured to sense the current flow through the load regulation device. A switching circuit is coupled to the sensor circuit and a logic circuit is coupled to the switching circuit. The logic circuit is configured to activate the switching circuit in response to the occurrence of a short circuit event. The logic circuit is also configured to deactivate the switching circuit after the load regulation device is substantially deactivated. A disable circuit is coupled to the switching circuit. The disable circuit is configured to deactivate the load regulation device when the switching circuit is active. The disable circuit deactivates the load regulation device by enabling a transistor in an output stage of the control circuit such that the load regulation device is deactivated, whereby the regulator circuit is protected from the over-current event.
Another embodiment of the invention relates to a method for providing short circuit protection to a regulator circuit that regulates a current flow through a load regulation device. The method comprises: detecting the occurrence of a short circuit condition, setting a latch to indicate the occurrence of the short circuit condition, disabling the load regulation device when the latch is set such that the current flow through the load regulation device is interrupted, monitoring the load regulation device to determine when the load regulation device is substantially deactivated, resetting the latch when the load regulation device is substantially deactivated, and enabling the load regulation device after the latch is reset such that the regulator circuit regulates the current flow with the load regulation device.
In yet another embodiment of the invention, an apparatus provides short circuit protection to a regulator circuit that regulates a current flow through a load regulation device. The apparatus includes a means for detecting that is configured to detect an occurrence of a short circuit condition within the regulator circuit. A means for setting a latch is configured to set a latch to indicate the occurrence of the short circuit condition. A means for disabling the load regulation device is configured to disable the load regulation device when the latch is set such that the regulator circuit is disabled. A means for monitoring the load regulation device is configured to determine when the load regulation device is substantially deactivated. A means for resetting the latch is configured to reset the latch when the load regulation device is substantially deactivated. A means for enabling the load regulation device is configured to enable the load regulation device after the latch is reset such that the regulator circuit regulates the current flow with the load regulation device.